I wouldn't categorize Picard as "grimdark". It certainly has grim tones to it at times, and has needlessly gratuitous scenes in it, so I get the complaint and understand it not being people's cups of tea. (I still resent a few very specific scenes myself.) But being grim is thematically not the objective of the narrative, but rather the context of the themes which still very much remain hopeful and positive. That's really a common complaint against nuTrek I see in general, and it doesn't feel like a fully considered critique when the context is overlooked. To me, grimdark things are just sad/depressing for the sake of being sad/depressing alone. But when it's ultimately in service to a larger narrative arc, especially one that is fundamentally hopeful and positive, that's an important distinction I think. The violence and brutality in Picard serve to inform why we would see certain characters in the show have made the choices in their lives that led up to that point, but PIC usually shows that in the service of advocating for being better/living up to lofty ideals, and characters are rewarded for doing so. In that sense, it's no different from some of the darker storylines in DS9, VOY, and ENT that generally get fan approval, IMO. To say nothing of films like WoK.
I also wouldn't say that the Federation as depicted is "callous, corrupt, and too much of an allegory for certain modern nation state governments" either. At least, not any more so than old Trek. There's no real obvious corruption in PIC beyond spies that have infiltrated Starfleet. And that's not unique to PIC. And the callousness is more a product of the Federation at this point in time being beleaguered by war and incalculable loss and the resources of Starfleet being spread too thin, than any willful intent. Both of these things were common Star Trek themes in the TNG-Era. The Maquis in particular say hello. But when presented with evidence and given a choice, Starfleet Command made the right decision and immediately dispatched a fleet to intervene and protect, which I don't think would be the case if they truly were callous and corrupt.
As for Picard's death, that's really a matter of perspective, I think. If you consider uploading your memory patterns into a robot to be a continuation of life, then I guess. I think there's a good argument though for that not being the case. IIRC Data himself argued in The Measure of a Man that even if you uploaded his memories into an identical machine, it would still not truly be him. Which is actually what informs his decision to have Picard pull the plug on him, because he views himself as having already died and thus come to the end of his natural lifespan. Picard as a character is not immediately bothered by such philosophical quandaries, but I get the feeling that this'll be an ethical issue that's explored in later seasons as he contemplates maybe he's just a soulless golem that thinks he's Picard.